When taking an x-ray of a patient, it is important to correctly position the x-ray source relative to the patient's body. Typically, the x-ray film is placed beneath a table on which the patient lies, with an ionization chamber positioned between the patient and the film. In order to ensure that the image formed on the film is in focus, the vertical distance of the x-ray source above the patient is set by the operator. Similarly, in order to ensure that the x-ray beam is incident upon the appropriate region of the patient's body, the x-ray source can also be moved by the operator in a horizontal plane.
Given the known dangers of x-ray exposure, it is important to confine the x-ray beam to that region of the body which is of particular interest. However, by utilising a smaller beam area the risk of missing the anatomical region of interest is increased. Failure to correctly capture an image of the area of interest will result in the need to take a further x-ray image, in addition to the wastage of x-ray film. Misalignment of the x-ray source in the vertical direction may also result in an out of focus image requiring that the x-ray procedure be repeated.
A known system for enabling accurate positioning of the x-ray source in the horizontal plane involves the projection of a beam of light from a light source onto a patient's body. The light source is positioned adjacent to the x-ray source and is fixed relative thereto. Typically, a x-ray radiation translucent mirror is used to direct the light beam onto the patient's body along the path taken by the x-ray beam. Prior to taking the x-ray, the operator positions the x-ray source using the light beam as a guide. Whilst in theory this system improves x-ray source alignment, in practice, regular checks must be carried out on the x-ray apparatus to ensure that the light source does not become misaligned relative to the x-ray source. Misalignment is common due to the strain placed upon the x-ray apparatus by constant movement. In addition, positioning systems of this type rely upon the expert knowledge and perception of a human operator to correctly position the light beam. X-ray images can be required for any part of the body and the operator may find difficulty in exactly centering the x-ray source to obtain a focused exposure.